4AGE 100kw flat spot and lurching when cruising

[85wrx]

I recently purchased a AE71 with 4AGE 100kw conversion. I have been gradually going thru and rectifying all the minor issues I saw and didn't like.

Lately it has been having an issue, the car seems to have a flat spot under light acceleration from 1500-2000 thru to 3000-3500rpm then acceleration hits hard. Try and push the throttle thru the flat spot and it will hit hard. Also whilst holding steady speed in all gears below between 2000 and 3000rpm, the car seems to be lurching back and forwards not holding a constant speed.

I have changed the following items in the last 2 weeks:
* Compete set of brand new spark plug leads inc coil lead (car died on a test drive. turned out to be a coil lead)
* New spark plugs platinum tipped BKR6EP-8 set at 0.8 mm
* Brand new TPS. Set throttle body and TPS as per manual with feeler gauges and particular resistance readings
* Swapped computers with no change.
* Swapped coils with no change.
* Set the ignition timing to either 10 deg btdc and 15 deg btdc no change. Tried to setup up with shorting terminals in diagnostic connector but it made no difference.
* New fuel filters
* I have also checked and there are no codes using CEL. (only code 42 for vehicle speed sensor).
* Fuel injectors have been serviced and cleaned.
* New water temp sensor fitted.

I decided to start again with the TPS. Disconnected it and went for a run, the lurching and flat spot have gone.

I have setup the TPS as per the manual again. Checked and double check all of the readings.
I then checked the voltage as per the 4AGE manual as well. Got the following readings
IDL-E2 throttle open should be 4.5-5.5v. I am getting 12.3v. Issue 1
VTA-E2 throttle closed should be 0.5v. I am getting 0.65v. Issue 2
VTA-E2 throttle open should be 3.5-5.5v. I am getting 4.15v. yeah
VCC-E2 throttle any position 4.5-5.5v. I am getting 5.0v. yeah.
I have also checked voltages at B ad B1 all good 12v.
I have swapped both the computer and TPS. Still getting the same results.
Anyone have any suggestions as what is causing this and how to fix it?
The manual has got me this far but not sure where to go now.

The interim fix is to leave the TPS disconnected but I want to sort what the problem really is.

[tottacrolla]

Ignoring the fsm settings for a while you could try setting the TPS with the engine running. Essentially the idle is managed by a separate map in the ecu and the ecu uses the idle switch in the TPS to access it.
So, run the engine at idle and turn the connected TPS and you should notice that the engine revs drop slightly when the idle switch is engaged. Set the TPS with the idle switch just engaged at idle.
Also check the wire connections are correct in the TPS plug.
http://charmant4age.blogspot.co.uk/search?q=ecu

What about MAP sensor ?

[85wrx]

So I guess this would be the same as getting the ohm meter on the IDL and E2 pins and rotating till you get an open circuit??
I haven't checked h MAP sensor. I don't think that will cause this.
Wiring is as per the 100kw wiring diagram.

[Matt]

Did you adjust the TPS?


https://www.youtube.com/watch?v=k7jS1y70S98

[tottacrolla]

When you short the contacts in the diagnostic connector does the engine slow down and does the timing stay locked ?
The throttle plate closes completely and the TPS was set when in this state ?

[85wrx]

Yes the TPS was set as per the manual with feeler gauges.

I am assuming you are talking about shorting to set the timing. If I short these contacts the engine speed doesn't change.

[tottacrolla]

If there is no change in idle speed with the diagnostic shorted then you are not getting idle mode in the ecu.
As I said earlier, ignore setting with feeler gauges for the moment and adjust the TPS until there is an engine speed change at idle.
Then check with the diagnostic for an engine speed change and error codes.
The speed change at idle with the diagnostic shorted is because the ecu fixes the ignition timing at 10 degrees BTDC to allow easy setting of the ignition timing. Typically the "un-shorted" timing will be 16 degrees.

[85wrx]

I set the TPS as you stated. It made part throttle cruising worse. So I set it just before the engine revs drop slightly. Seems to be best from all the settings I have used so far. Will test it for a couple of days and see what happens.
When you put the shorting lead in to adjust timing it will now change the engine revs slightly now.
Checked the error codes as well. No codes just blinking continuously about every 1/2 sec.

[tottacrolla]

I set the TPS as you stated.
No you did'nt.
Anyway... it sounds like you have got it to go into idle mode. Now it would be a good idea to re-set the ignition timing as per the manual.
Once you have driven it you will likely get the speed sensor error code back and it will show the light on the dash over a certain speed / revs.
I guess you have a knock sensor fitted as you are not getting an error code ?

[85wrx]

If I didn't set the TPS how you stated, how am I supposed to set it?

From the earlier post from you, you said to rotate the TPS till the revs drop. Which is what did. This made it worse.

Looks like the issues hasn't been resolved. It is still doing the same thing. Yes the knock sensor is connected.

[85wrx]

Disconnected the TPS and drove the car all day. With it disconnected the car had smooth acceleration, no surging and no flat spot.

Weird thing is the CEL did not illuminate. I haven't had the chance to see if there are any codes.

I don't want to leave it disconnected. Prefer to sort out what is causing this issue.